1. Field of the Invention
The invention concerns writing tablets, each sheet of which bears a pressure-sensitive adhesive pattern by which the sheet can be adhered to an object, either temporarily or permanently, depending upon the qualities of the pressure-sensitive adhesive.
2. Description of the Prior Art
An office supply item in widespread use is a tablet of individual paper sheets, each bearing a narrow band or stripe of low-tack pressure-sensitive adhesive by which the sheets can be temporarily adhered to documents or other articles, usually for message-bearing purposes. In the most popular of these tablets, every adhesive band extends along one side of the tablet. In another such tablet, the adhesive bands extend along alternating opposite sides of the tablet, thus creating a Z-stack as illustrated in U.S. Pat. No 4,416,392 (Smith). Tablets of each such form are currently being marketed under the trademark "Post-it" by the company to which this application is assigned. Useful low-tack adhesives based on tacky, elastomeric copolymer microspheres are disclosed in U.S. Pat. Nos. 3,691,140 (Silver) and 3,857,731 (Merrill et al.)
To make such a tablet using an aggressive pressure-sensitive adhesive would require a release coating on the nonadhesive, message-receiving face of each sheet, and such a coating inhibits the acceptance of inked messages. Even when the pressure-sensitive adhesive is low-tack, the underlying face of each sheet usually has a release coating to insure perfect removability after prolonged storage.
Some such tablets have a printed message and/or decoration on each sheet, but to do this mechanically has required printing of the sheetstock before the tablet is formed. In order to apply such printing after the tablet has been formed, it has been necessary to peel off and imprint each sheet separately, e.g., by temporarily adhering one or more sheets to a piece of paper and loading this into a typewriter or copier.
3. Other Prior Art
UK Patent Application No. GB 2,150,883A shows a "continuous blank form", e.g., a pin-drive paper web which can be automatically printed in a computer. After being printed, the form is designed to be torn apart into pieces that can be folded and sealed to form an envelope around the printing. Each piece has tracks of a "cold adhesive" such that a strong bond is formed when the tracks are pressed against each other, but the adhesive tracks do not adhere to bare paper. The adhesive tracks are aligned to contact each other upon folding, and upon doing so, it is said that "the letter cannot be opened without leaving traces". Although not illustrated, it is said that the continuous form can be kept in an accordion-like stack or a zig-zag pile (fanfolded) by offsetting the adhesive tracks so that they do not contact each other and hence do not inhibit unfolding. See page 2, lines 62-93, and the abstract on the cover sheet.
U.S Pat. No. 4,460,634 (Hasagawa) concerns an adhesive sheet which can be removably mounted onto a panel, wall or the like for display purposes. A typical adhesive display sheet as shown in FIG. 1 comprises circular adhesive pieces 2 which are made by "pasting an adhesive agent in selected areas on the rear face of adhesive sheet 1" (col. 3, lines 59-61). Circular nonadhesive plastic support pieces 3 are secured to the adhesive sheet 1 between adjacent adhesive pieces and preferably "have substantially the same thickness as the adhesive pieces 2" to enable the sheet 1 to be easily peeled off a panel or wall. As illustrated in FIG. 15, a similar sheet 1a' which carries a checkerboard of adhesive squares 2a and support portions 3 can be folded along line 9, because the adhesive squares 2a of each half of the sheet contact the support portions 3 of the other to permit the two halves to be peeled apart. The description of FIG. 15 concludes by stating that the folding line 9 may be replaced by a perforated line (col. 9, lines 20-21).
UK Patent Specification No. 1,594,798 shows a "continuous stationery envelope assembly" which is "divided into individual envelope lengths by transverse lines of cross perforations" (claim 1). At the periphery of each envelope is a band of hot melt or heat seal adhesive.